Corebarrels are used in oil and gas exploration to retrieve core samples to provide the user with information on the stratigraphy of the rock formation which is to be drilled.
Core samples are normally cylindrical sections of formation of the order of a few inches in diameter and from 30 to 90 feet in length.
In some wells at considerable depth gases may be trapped within the rock formation and become dissolved in the said formation under the extremely high pressures. As the core sample is raised out of the well the pressure on the sample reduces and any such formation gases may revaporize resulting in a positive gas pressure within the corebarrel.
Such increased pressure within the core barrel can be a considerable problem for a number of reasons. Firstly, if there is any gas impermeable layers, such as shale, above and below a layer containing pressurised gas then the gas will not be able to escape and may result in bulging of the core sample. Such bulging normally results in the core sample being stuck within the outer casing of the corebarrel. Also sudden release of the gas when the corebarrel is removed to the surface can result in explosion.
It is an object of the present invention to provide a system which enables the safe release of formation gases when the corebarrel is being raised.